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They say milk does a body good - but that's not the finding of a recent study conducted by researchers at Kaiser Permanente in California and the University of Utah. In a recent study conducted among 1,849 women who had been diagnosed with breast cancer, the researchers found that consuming high-fat or full-fat dairy products increased women's risk of relapsing or dying of breast cancer.

The study was conducted over the course of 12 years using women who had been diagnosed with early-stage invasive breast cancer. The women all answered a questionnaire about their eating habits over the past year. Six years later, about 1,500 of the women answered a follow-up questionnaire about the same topic. In total, 349 of the original women saw their breast cancer recur after treatment, while 372 women died. Half of those women died of breast cancer.

The BBC reports that researchers found that women who ate one or more servings of high-fat dairy a day - which included milk, cheese, yogurt, ice cream and other dairy products - had a 64 percent increased risk of dying from any cause. The same eating habits were associated with a 49 percent risk of dying from breast cancer. They also found that the link was weaker with saturated fat, indicating that it was not saturated fat, but the type of fat specifically found in dairy that is responsible for boosting the risk of breast cancer.

However, eating low-fat dairy products was not associated with any preventative benefits.

Experts say that some of the problem is likely linked with ingesting too much estrogen. Previous studies have found a link between too much of the sex hormone estrogen with breast cancer. That link is particularly strong for estrogen receptor positive breast cancer, the most common type of the disease.

"In western countries they manage to breed cows and modify them so they can be pregnant at the same time and give milk, which means the milk has more estrogen," Candyce Kroenke said to Everyday Health. "It's this particular method of production that leads to the level of hormones we're talking about in the study."

The study was published in The Journal of the National Cancer Institute.